A. It became effective when Gov. Pat Quinn signed it Jan. 13. The increase is retroactive to Jan. 1.

Q. How much more can I expect to pay?

A. The individual tax rate in Illinois increased from the current 3 percent to 5 percent. A person who previously paid $1,000 in state income taxes pays $1,660 under the new rate. A person’s actual tax liability depends on multiple factors, including income and deductions.

Q. When will I see the effect of the tax hike on my paycheck?

A. You should have already. It depends on how quickly individual employers implement new withholding schedules. The Department of Revenue issued those new schedules to 300,000 employers and posted the information on its website.

Q. The tax hike is retroactive to Jan. 1. Does that mean my employer is taking a bigger chunk out of my check to cover what wasn’t withheld the first couple of weeks of the year?

A. No, says Department of Revenue spokeswoman Sue Hofer.

“We don’t expect employers to withhold extra money to cover the first one or two paychecks already received by their employees,” she said.

Q. Does that mean I get a break on the first couple of weeks of the tax hike?

A. No again — the state will get its cut eventually. When you file your 2011 tax returns a year from now, the tax schedules will reflect the increase. If you normally have to pay an additional amount to the state as part of the return, you may have to pay a little more. If you normally get a refund, it may be a little less to compensate for the tax hike. Either way, state officials said the impact shouldn’t be significant because the changes are taking place early in the year.

Q. How do corporations handle their tax increase?

A. Corporations are required to make estimated tax payments to the state four times per year. They’re being advised on how to adjust those payments.

Q. Are the increases permanent?

A. The bill approved by lawmakers stipulates the increase is temporary while the state fights its way out of its budget problems. After four years, the individual rate is scheduled to drop to 3.75 percent. Beginning in 2025, the individual rate is scheduled to drop to 3.25 percent.

Illinois has had two previous temporary income tax increases. One was allowed to expire, while the other was made permanent.